Image by Capture Queen ™ via Flickr
No idea is proven to be a good or bad idea until it proves itself.
It takes discipline to hear ideas from others. First, you have to listen when you may not want to. Second, you have to respond in a way that doesn't tear down their momentum or desire to work with you again in the future. That person may be a door you don't want to close. It's easier to dismiss an idea and move on, but don't fall in to that trap.
Let your initial response be sincere and positive. If there are holes in the idea, it's likely they will be discovered on their own pretty quickly. There's no need for you to point them out and walk away from pooping on the dream.
The key is to take the ideas presented to you and develop them together. Make it better. Put your fingerprint on it. Improve it so that everyone can take ownership. If your first response is, "I don't like it," and that's all you say, you miss out on opportunity. You may lose respect too.
If you want people to listen to your ideas, then prove that you can contribute to theirs.